What elements end up making the U.S. the most ethnically diverse society in the world?

I would say that one of the most profound elements that contribute to American diversity would have to be immigration. The narrative of American immigration, something that still is intact despite a recent reevaluation of policy, is that America represents "the land of opportunity." Realities might have changed in the world, but it seems that this maxim is still valid in that so many seek to come to America in the hopes of a new life. The lack of institutional hierarchy in America and its own history as a nation that takes the discarded from other nations only to see them improve both themselves and the quality of the nation, in general, are elements that help to make America an ethnically diverse society. Given how so many come from so many different nations, there is not a full fledged identification of what it means to "be American." Rather, the term "American" is accepted to represent beliefs and ideas, elements that nearly anyone can appropriate. "American" can apply to any group of people who live in the nation and participate in the full extent of its promises and possibilities. American states are all experiencing a greater influx of people who carry with them different narratives and backgrounds. All of these fall under the umbrella of "American," and in this, one sees how the nation is the most ethnically diverse society in the world. As long as the concept of "being American" is tied to the experience of being in America, the nation will continue to be diverse because it will attract people who live in parts of the world where the identification of ethnicity and nationality carry implications of displacement and rejection. This is where America provides an automatic magnet for such individuals.